Alcholeplasma laidlawii has been found to be associated with the induction of interferon (IF) in ovine peripheral blood leukocytes. This observation will be extended utilizing interferon induction as a probe to investigate mycoplasmal-cell interactions with particular emphasis on peripheral leukocytes and cells of the reticuloendothelial system. More specifically it is planned to determine: 1. To further define the specificity of mycoplasma-cell interactions which may result in induction of interferon. a. cell type responsible for interferon induction using sheep donors. b. induction of interferon by species of mycoplasma other than A. laidlawii. c. induction of interferon by various animal species (man and mouse) 2. To elucidate the mechanism of induction of interferon. a. determination of requirement for viable, inactivated or disrupted mycoplasmas. b. role of sensitized lymphocytes in induction of interferon. c. requirement for adsorption and/or cell penetration. d. role of Mycoplasmatales viruses in interferon induction. 3. To investigate the in vivo induction of interferon by mycoplasmas. a. can mycoplasmas induce interferon in vivo? b. are mycoplasmal viruses responsible for the in vivo induction of interferon? c. do mycoplasmas alter the susceptibility of mammalian hosts to viral infections?